First Night Out
What About a Telescope?
Upclose without a Telescope
After the Photo Session
I have been asked to do a write up of my experiences and tips for getting started in astrophotography. Since I currently only I currently only do astrophotography without the use of tracking, I figure this is the best place for me to begin. In 2007 I took an intro to Astronomy class and I was hooked. Soon after, I bought a telescope (6″ Dobsonian) and a camera (Canon 350D) plus some adapters and went to town. I wish I could say that the experience was breath taking. Well, in some ways it was, as in making me so frustrated I felt like I couldn’t breath at times. Thirteen years later I feel like I have made enough progress to give a short primer on taking photographs of the night sky, and hopefully it helps side step some of the frustrations I had early on.
I have said this in a previous post, but the first thing you should do is learn the night sky. There is no point in taking pictures of things that you don’t know what they are. Yes, there are some spectacular wide angle photographs of the Milky Way by people who don’t know the first thing about the night sky, but believe me, taking the same picture over and over again, just for the sake of taking a picture for likes on Instagram, will get old quickly. So, get a star chart – available as pictures on line, or for purchase, and go out and look up!
The next thing you are going to want is a camera (and a good tripod). Since we have not even begun to bring up telescopes yet, we are looking at a Digital SLR or something very similar. On the flip side, your cellphone may also be an amazingly viable option, especially for starting out. I personally use a Nikon d610 and a Nikon CoolPix p950. Even though the p950 is not a DSLR, it will enable me to shoot in RAW and because of it ease of use, I like to use it for wide angled night sky shots.
Above are some photographs taken with the Nikon p950 with the lens set at 185mm, exposure set at 2 seconds, ISO at 3200 and aperture at 4.5. Now, if none of that meant anything to you, then you have another job before getting started on the next step – Learn how to use the camera you have (and learn the terms and functions!) To answer the question you are about to ask, Yes, you need to become an astronomer and a photographer! Luckily you don’t need to know astrophysics or spend thousands of dollars going to school for photography, you just need to know the basics of both disciplines.
Now that you know the night sky well enough to at least find the bright stars (and realize which direction they are moving) and you also know your camera well enough to be able to determine what focal length you are using, aperture, exposure, etc, let us set up some initial photo shoots.
So far, we have taken some time to learn the night sky as well as get a camera and lens, if a DSLR, and now we are ready to begin taking pictures of the night sky. Before moving forward, I want to mention two methods of taking pictures that are very important. The first is simply taking a single photograph and moving on. The second is taking multiple pictures of the same region of the sky and then taking them and stacking them to make one image. All four pictures above are stacked images and the results are a lot better then what they would have been if it was just a single frame. Now, it is possible to take a wide angle (24mm – 50mm) shot with a high enough ISO and long enough exposure to get a really nice shot if you are in really dark skies. However, if you take the time to learn how to stack photographs (especially now!) it will make things a lot easier for you in future endeavors, plus make your. Also, stacking plays a huge part in being able to take a more “zoomed” in photograph and bring out detail. For this exercise, I am going to assume that we WILL be stacking.
Its Summer, so we are going to find Vega (Bright, to the East and closer to Zenith then the horizon, so easy to find even in a city). We are going to set up our camera on the tripod, point it at Vega and based upon what type of lens we are using, set our camera to settings that will enable us to take a shot of Vega that will contain as much data as possible without having star trails. The main issue is going to be our exposure length and we are going to set that based on what focal length our lens is.
In astrophotography we have what is called the “500 Rule” – this states that in a full frame camera, you take 500 and divide it by your focal length to get the maximum exposure you can use before you start getting trails in stars. For example, shooting at 24mm puts you around 21 seconds. You would round down to 20 seconds. If you have a full frame sensor in the camera you bought then you can use your 24mm lens and take a picture of Vega with an exposure of 20 seconds and there will be no (or very minimal) star trailing. For sensors that are not full frame, you may need to use 400 instead of 500 (making you 24mm exposure 15-16 seconds). You will want to experiment to determine what works best for you in the end Here is a document (exposure times) that I put together for my own personal use with my Nikon P950.
Next you are going to want to determine what ISO and aperture you are going to use. If you are using a DLSR with a lens, that aperture may be fixed, or it may have a range. Typically, anything f4.0 or “lower” (1.4 – 4.0), with the lowest possible, is better. For example, if you are shooting at 50mm and can pick between 2.8 and 3.5, pick 2.8. For ISO, since we are stacking, choose between 3200 and 6400. Note: in really dark skies with cameras that have really good sensors, you can go even higher. With my camera, and where I normally (in Providence, RI) take pictures, I stick to 3200 ISO. If I can get to darker skies, I use 6400 ISO. Even with heavy light pollution (Providence is a Bortle 8 – click here for an explanation on the Bortle Scale) you can still use a decently high ISO due to the fact you will be stacking frames.
Now that we have an idea of how to setup, here is how we are going to do its: (I am going to base this off of settings I use with my P950)
1: Lens – 80mm
2: ISO – 3200
3: Exposure: 6 seconds
4: Aperture: 3.5
1: Lens – 50mm
2: ISO – 3200
3: Exposure: 10 seconds
4: Aperture: 3.5
1: Lens – 185mm
2: ISO – 3200
3: Exposure: 2.5 seconds
4: Aperture: 4.5
For all three setups we are going to use manual focus and put it on Infinity focus.
Now, as you can see, as the focal length of my lens changes, so does my exposure and my aperture. I use the lowest possible aperture based upon the focal length that my camera / lens allows and adjust my exposure according to the 500 Rule so I don’t get any trailing in my stars.
Now that I have my setup, I am going to use #2 and set my sights on Vega. I put a time of 3 or 5 seconds (depending on my camera) so I don’t translate any shake from pressing the shutter (you can also use a remote shutter release, many new cameras even have an app for your cell phone!) and I take a picture. The picture is going to look a little bright, and even a little fuzzy due to camera noise. I use the zoom feature on my camera’s playback to check two things: focus and trailing. I notice no trailing but the focus can be a little better. Make a small adjustment to focus and shoot again. This time focus is good! Now we are ready to take a series of shots / frames for stacking. While taking shots, we are going to have to adjust our camera’s position slightly every minute or so (at 50-80mm), every 30 seconds or so (185mm) or maybe after every shot (200mm and above) to make sure we keep what we are taking pictures of in the frame and as close to each other as possible. This is so we a) make the stacking as easy as possible and b) when we do stack, we get as big a picture as possible containing all the same data. Vega is a good place to start because you can see it in the view finder and mentally mark where it is and make adjustments as needed. We want to take as many pictures as possible – I like to take 40+ and come as close to 100, especially on the ones I do at 185mm since I am only exposing for 2 – 2.5 seconds. Once we get all of the frames that we are going to, we need to make what is called dark frames. These are done simply by putting the lens cap back on the camera lens and taking pictures with the exact same settings as the “light” frames. Personally, I like to make 20 dark frames at minimum, and if I shoot more then 100 light frames, I then go to 30 or 40 dark frames. There are also other processing frames you can make: Bias and Flats, but I am not going to cover those extensively right now (I hardly use them myself). Flats are basically shot in AV mode and are done to help remove artifacts, such as dust on your lens, off of your photographs. Bias frames are Dark frames that are shot at the quickest exposure possible while all the other settings remain the same (e.g. 1/2000 exposure, or quicker depending on the camera).
Now, we have our light and dark frames. For this write up lets say we got 80 light frames and 20 dark frames. Use your camera’s software to go through the light frames and pick out any that are noticeably bad. This could be that the focus messed up, or clouds came into view. Anything that makes it noticeably bad is a good reason to get rid of it. Delete those. Now for stacking – I like to use a program called Siril for stacking my wide angle night sky photographs. Siril can be downloaded here and works on both PC and Mac. I recommend watching a tutorial on using Siril – a good one is this YouTube video. Though it covers pictures taken through a telescope, everything mentioned applies to the photographs we just took. There are other stacking and processing programs out there – and I use some of them for other applications, such as when I do planetary photography, but for wide angle, this is the program I prefer.
Once you follow the directions and do some minor processing (as shown in the video) you should have a decent photograph of Vega / the constellation Lyra, congratulations!
In my opinion, once you have learned the night sky, learned your camera and gotten comfortable with taking photographs of the night sky, it is time to move on to the more challenging, yet very rewarding, task of taking pictures through a telescope. For the most part, without tracking, you are going to be “stuck” with taking pictures of the Moon, planets and the sun (with the proper filter).
Getting Started with a Telescope guide
For lunar and solar photography, it really is as simple as connecting a camera to an eyepiece, or even directly to the telescope focuser itself (prime focus), finding focus, finding the right exposure and taking the picture. For planetary, it is often best to take video of the planet, convert it into individual frames, then stacking those frames (like we did with the wide angle shots) and doing some processing to finish the image. Though prime focus is best at times, a lot of telescopes cannot achieve it without help: either using a lens called a barlow, or by moving the primary mirror forward (advanced!) can help achieve focus this way. Typically, using an eyepiece and attaching your camera, or even your cellphone to it, can produce some amazing pictures. It can even take good enough video to get planetary images. Of the four pictures above, all but the sun, which was taken with a Nikon d610 through a 32mm eyepiece, were produced with a cellphone (Samsung Galaxy S9). The moon shot was taken with a 14.5mm eyepiece and the cellphone zoom was used (1.7x) to get the closeup shot. For Saturn and Jupiter, a 9mm eyepiece with a 2x barlow lens, attached at the bottom of the eyepiece barrel, was used. Saturn was about 2 minutes worth of video, Jupiter was around 3 minutes.
To get started, you need to decide what you want to take a picture of. If its is the Moon, then what we want to do is take an eyepiece and attached a camera to it. To do so, you will need to get an adapter. TelescopeAdapters.com have a wide arrange of such adapters, each suited to different cameras and setups. I have not ran into a situation yet where they did not have an adapter, or a group of adapters, that did not fit my needs. If you are using a DSLR, you will need an adapter called a T-Ring that attaches where your lens normally would as well as a smaller ring that fits on your eyepiece that will then screw into the T-Ring on the camera.
If you would rather try prime focus – connecting your camera to the telescope without an eyepiece, you will need the T-Ring as well as a prime focus adapter (essentially the smaller ring with an extension that fits into the telescope’s focuser. If you cannot reach focus this way, adding the lens portion of a barlow lens may help you. Simply screw it into the bottom of the tube on the prime focus adapter.
Another option is to use a lens filter adapter to attach the eyepiece to your camera but with the lens still attached to the camera itself. This enables you to shoot with your existing camera lens through an eyepiece. This is called afocal photography.
A couple of notes on afocal photography. This is the only way to do photography through a telescope with point and shoot camera or a cellphone. You must be careful of the camera’s vibration when it takes the picture. Because of this, it used to be that the only way to do afocal was to set a camera on a tripod and place it close the the eyepiece. This can still be the case, but many modern cameras have a lot less vibration then they used to. For a cellphone, instead of using filter ring adapters, you can purchase an adapter that hold the cellphone and fits on the eyepiece.
Something to note, not all point and shoots work well attaching to an eyepiece. The Nikon P950 is one of these that does not. If you plan on doing afocal with a point and shoot camera, do some research online first to determine if the one you own will work well.
This type of adapter will fit most eyepieces, though some more expensive/premium ones may need to be adapted (depending on the cellphone adapter) or finagled a but to get them to fit/hold to the adapter. I currently tale the majority of my pictures and videos this way!
Above is a picture taken with the afocal method through a 25mm eyepiece in a 6″ Dobsonian telescope. I used a Canon A75 point and shoot camera and simply held the camera up to the eyepiece. You can do this with a cellphone as well!
The last type of telescope photography to talk about is called eyepiece projection. This is where an eyepiece either attaches at the bottom of a tub or sits inside a tube and the camera attaches to the opposite end. The tube is split and the top half can slide up and down to provide further magnification beyond what is normally possible by just attaching the eyepiece to the camera.
I find that this type of photography, when not using tracking, is best for lunar and solar photography.
Once you have a telescope, good eyepiece and the adapters you need, the key is to experiment with both your equipment and your settings.
These two pictures were taken literally three weeks apart. The first one is a single shot, using eyepiece projection and a DSLR. The second picture is a stacked photograph using a cellphone and a 9mm lens with a 2x barlow and a moon filter (I know, I haven’t mentioned filters before now). With patience, experimentation and research, you can make lot of progress in a short period of time!
When it comes to settings, what matters exclusively is what you are trying to capture. For the moon, your shutter speed will be around 1/250 – 1/500. Your ISO will be around 200. Your aperture, unless using a lens, will be that of the telescope. For taking video of Jupiter, you may have to go with your camera’s stock settings, using filters if needed to lower the brightness. If you cellphone has a pro mode, then use it, adjusting your aperture, ISO, etc as needed. The biggest issue will be your focus. Always use manual focus and do as light adjustments as possible to your telescopes focuser as you can once you get it close. You will be amazed how a slight turn can make a huge difference.
4 – Upclose without a Telescope
My 6″ and 10″ Dobsonians have a focal length of 1200mm. That is pretty good when it comes to how much you can magnify an object. At prime focus, the magnification is around x24. When I use a 25mm eyepiece, I get a magnification of x48 (focal length of telescope divided by focal length of eyepiece: 1200/25). That is pretty good for viewing the moon. A 2000mm lens gives me a magnification of around x40 (focal length divided by 50). This means I can use a 2000mm lens to get telescopic photos of the moon!
These pictures were taken with my Nikon P950 at 2000mm, 400 ISO, aperture of 6.5 with an exposure of 1/500 of a second. I took several pictures and dark frames as detailed before and stacked them to get these results.
As mentioned before, I use Siril to stack and process my wide angle night sky photographs. Here are some more programs that are useful:
1 – AutoStakkert – I use this to stack my planetary an lunar photographs
2 – PIPP – I use this to convert my videos to a format that AutoStakkert can use (.avi)
3 – Registax – I use this to process my planetary pictures by using the wavelets function once they are stacked
4 – Photoshop – I use this mainly for processing my moon photos once they are stacked, or if I am using a single shot from my cellphone. I also sometimes use it to process other images depending on the end results from using Siril or Registax
All of these programs, except Photoshop, are free, which is really nice! There are other programs you can use, some free, some you have to pay for. There are also Photoshop plugins you can get – typically have a cost – that do a lot of processing things as well.
This is a lot longer of an article then I planned on writing, and unfortunately, I probably could have made it twice as long! Astrophotography seems daunting, and it can be frustrating, but it is not as difficult as it may seem. You can do a lot with very little, and sometimes the smallest thing will make a huge difference. As an example, simply by taking video of Jupiter and Saturn instead of trying to take single shots, my planetary photography increased 100 fold!
Here is a progression of Saturn (again over a period of around a month! The really awesome part in everything I have told you today is that these types of photographs can be taken without any sort of tracking – other then making adjustments by hand – at all. All you need is a decent telescope, a cheap adapter and a cellphone and you can begin taking some pretty amazing photographs. The more you invest, both in time and money, the better your pictures will get. If and when you decide to take the leap into tracking, you will be a step ahead with the knowledge you have gained.
High Point Scientific
Digital SLR Astrophotography – Michael Covington
The Astrophotography Manual – Chris Woodhouse
Peterson Field Guide – Stars & Planets
Field Guide to the Night Sky – Audubon Society
Starry Night – Astronomy & Telescope Sofware